The present invention relates to organophilic clays. More particularly, the present invention relates to organophilic clays that comprise a smectite clay modified by reaction with a protonated amphoteric surfactant, and methods for the preparation and use thereof.
Organophilic clays may be used in a wide variety of subterranean applications. As used herein, the term “organophilic clay” refers to a clay that is compatible with oils. In subterranean applications, organophilic clays are widely used, for example, in various cementing and sealing operations as well as to add viscosity and/or suspending power to various fluids. In addition to subterranean applications, organophilic clays also may be used in a variety of surface applications, for example, as a viscosifying agents, suspending agents, and the like.
In some instances, organophilic clays may comprise a smectite clay that has been modified by a cation exchange reaction with a fatty quaternary ammonium surfactant. Generally, the quaternary ammonium surfactant imparts some organophilic character to the clay. However, this class of chemicals has proved challenging from an environmental standpoint. For instance, the quaternary ammonium surfactants used heretofore may have undesirable environmental characteristics and/or may be limited by strict environmental regulations in certain areas of the world. As a result, use of these quaternary ammonium surfactants in subterranean applications may result in the potential for the bioaccumulation and/or persistence of the quaternary ammonium surfactants in the environment, which may create potential dangers for the use of the quaternary ammonium surfactants, such as adverse effects on shrimp and other aqueous aquatic species. Accordingly, in more environmentally sensitive regions, such as the North Sea, quaternary ammonium surfactants generally are not acceptable, and therefore the use of organophilic clays produced using quaternary surfactants is also not acceptable.